Field of the Invention
The present invention relates to a method for producing an electrophotographic photosensitive member.
Description of the Related Art
An electrophotographic photosensitive member obtained by forming an undercoat layer (intermediate layer) and a photosensitive layer on a support in the stated order is often used as an electrophotographic photosensitive member to be used in an electrophotographic apparatus. The undercoat layer is generally formed by forming a coat of a coating liquid for an undercoat layer containing a binder resin and drying the coat.
The incorporation of metal oxide a particle and the binder resin into the coating liquid for an undercoat layer has been frequently performed for the purposes of concealing a defect of the support and suppressing interference fringes generated by interference between exposure light beams. Further, a titanium oxide particle out of the metal oxide particle is suitable as metal oxide particle to be used in the undercoat layer because the particle has high refractive index and hence exhibits a high scattering effect.
In addition, the binder resin to be used in the undercoat layer is required to have resistance (solvent resistance or insolubility) against a solvent to be incorporated into a coating liquid to be applied above the undercoat layer (such as a coating liquid for a photosensitive layer (a coating liquid for a charge-generating layer or a coating liquid for a charge-transporting layer)). In addition, the undercoat layer is required to have durability against repeated use of the electrophotographic photosensitive member, and such environmental resistance that images can be stably formed under various environments ranging from a high-temperature and high-humidity environment to a low-temperature and low-humidity environment. From such viewpoints, a curable resin is suitable as the binder resin of the undercoat layer. Further, a curable resin capable of being cured at low temperature (production of the curable resin at low temperature) is required from the viewpoint of productivity of the electrophotographic photosensitive member.
With regard to a resin satisfying the foregoing requirements, Japanese Patent Application Laid-Open No. 2004-198734 discloses a technology involving using a curable resin (urethane resin) obtained by causing a blocked isocyanate compound having an isocyanate group blocked with a diethyl malonate structure and a polyol resin to react with each other, as the binder resin of an undercoat layer. The isocyanate group of an isocyanate compound is sometimes blocked with a blocking agent from the viewpoint of controlling its reaction, and the isocyanate compound having a blocked isocyanate group is referred to as “blocked isocyanate compound.”
However, as a result of their investigations, the inventors of the present invention have found that such a problem as described below occurs. That is, the inventors have found that a viscosity of a coating liquid containing a blocked isocyanate compound having an isocyanate group blocked with a structure represented by the following formula (1) (alkyl malonate structure) or a structure represented by the following formula (2) (β-ketoester structure), and a polyol resin increases with the lapse of time in some cases.